Clear imaging of ion cloud rotation using a combination of a thin metal wire, a micro-channel plate attached to a phosphor screen, and a high-speed camera

To obtain the radial profile of the ion velocity ui(r) of a pure ion cloud, for the first time, we successfully captured images of the shadow of a thin rotating metal wire by scanning the pure ion cloud using a combination of a micro-channel plate attached to a phosphor screen and a high-speed camera. It appears that the rotation angle of the measured metal wire agrees with the estimated value based on the theory of two-dimensional equilibria of non-neutral plasmas, rather than the magnetron motion of a single ion confined in a Penning trap. This method may be utilized as a tool to experimentally investigate ui(r, t) in electrically non-neutral two-fluid plasmas, which is an unexplored topic in advanced plasma physics.